Barrier coatings (layers) which prevent, reduce, or inhibit the permeation of a selected substrate with a gas, vapor, chemical and/or aroma have been widely described, and such coatings are used in a variety of industries, e.g., the packaging industries, automobile industries, paint industries, tire industries etc. Typical barrier materials used in coatings include polyesters, PVDC, polyurethanes, acrylic polymers, etc.
It is well known that the barrier properties of a polymer can be improved by the addition of impermeable plate like structures such as kaolin, vermiculite, montmorillonite and so forth. When the plates are oriented perpendicular to the diffusion (permeation) direction, the diffusing molecules must go around the plates. This leads to significant reductions in the permeability of the polymer. See, for example, E. L. Cussler et al, J. Membrane Sci. 38:161-174 (1988); W. J. Ward et al, J. Membrane Sci., 55:173-180 (1991); Chang, J. et al, Journal of Applied Polymer Science, Vol. 84, 2294 (2002); Yano, K. et al, Journal of Polymer Science A: Polymer Chemistry, 35, 2289 (1997); Lan, T. et al, Chem. Mater. 6, 573 (1994); Messersmith, P. B. and Giannelis, E. P, Journal of Polymer Science A: Polymer Chemistry 33, 1047 (1995); U.S. Pat. Nos. 4,528,235; 4,536,425; 4,911,218; 4,960,639; 4,983,432; 5,091,467; and 5,049,609; and International Patent Application No. WO93/04118, published Mar. 4, 1993, among others.
Some particularly preferred nanocomposite gas barrier coatings are disclosed in the following: U.S. Pat. No. 7,078,453, entitled “Barrier Coating of a Non-Butyl Elastomer and a Dispersed Layered Filler in a Liquid Carrier and Coated Articles”, to Feeney et al.; U.S. Pat. No. 7,119,138, entitled “Barrier Coating of a Mixture of Cured and Uncured Elastomeric Polymers and a Dispersed Layered Filler in a Liquid Carrier and Coated Articles”, to Feeney et al.; and U.S. Pat. No. 7,473,729, entitled “Barrier Coating Mixtures Containing Non-Elastomeric Acrylic Polymer with Silicate Filler and Coated Articles”, to Feeney et al., as well as copending United States Patent Applications Publication Nos. US 2007/0213446, entitled “Barrier Coating of a Non-Elastomeric Polymer and a Dispersed Layered Filler in a Liquid Carrier and Coated Articles”, of Feeney et al.; US 2008/0131707, entitled “Concentrated Aqueous Nanocomposite Dispersions for Barrier Coatings”, of Feeney et al.; and US 2006/0110615, entitled “Multilayer Nanocomposite Barrier Structures”, of Karim et al., the disclosures of which are incorporated herein by reference.
Despite many advances in the art, composite barrier coatings tend to exhibit performance degradation due to elevated relative humidity. The present invention provides coatings which resist such performance degradation upon exposure to elevated levels of relative humidity.